This invention relates in general to the construction of filters and in particular to a new and useful method and apparatus for producing a filter with multiple folds.
The invention concerns a process for producing a filter with multiple folds from an aqueous fiber mixture that is applied to one side of a porous form by which a paper-like filter mat is produced on the form by the action of pressure. Features of a tool for the preferred implementation of the process are also described.
Seamless filters, for example dust filters in respirator filters, are produced according to German Patent No. 727 678 from a truncated conical porous intermediate product that is turned up on a mold corresponding to the desired number and shape of the concentric folds. The filter tissue is severely flexed during the folding process, and under some circumstances it is predamaged to such an extent that cracking occurs. The thickness differences in different regions of the folds of the filter that form during the folding process are also a problem.
An annular filter is disclosed by DD Patent No. 79 that is cast in its final form from a fibrous slurry. Preparing a uniform, one-piece casting seems to be tedious.